The present invention relates generally to conveyor systems and has particular reference to an intermittent or step-by-step conveyor system which is designed primarily for handling sand molds in a foundry casting operation of the like and wherein the unpoured molds are conducted on individual pallets through various mold-handling and treating stations to a mold discharge station where the poured and partially cooled and solidified mold-encased castings are ejected from the system for shake-out purposes. It is conventional for foundries to have automated conveyor systems which intermittently advance sand molds from a mold making station, through a cooling section of the conveyor, to a jacket and removal station, and through other operations stations until the metal casting is finally removed from the disintegrated sand mold. These systems involve the problem of removing the jacket and weight from each partly cooled mold and its solidified casting, and transporting to another portion of the conveyor and subsequently applying the jacket to a freshly formed green sand mold approaching the pouring station. A mold-handling system of the general character under consideration usually requires jacket-setting because in making a casting, when molten metal is poured into a sand mold to produce the casting, the outward pressure on the mold walls may cause mold rupture so that what is commonly referred to as a "run-out" of the metal takes place. It is common practice to surround each mold with an encompassing metal jacket which will withstand such outward pressure on the mold walls, the jacket being placed upon the cold mold prior to the pouring operation and such pouring operation taking place with the jacket in position on or around the mold. Subsequently and after a predetermined cooling period has elapsed so that undue outward pressure on the mold walls is alleviated, the jacket is removed and the mold-encased casting is then ready for the usual shake-out operation for effecting removal of the mold from the formed casting.
The use of curvilinear or serpentine type mold-handling system has been said to be possessed of certain limitations, principal among which is the necessity for utilizing a relatively complicated jacket transfer mechanism which is capable of transferring a jacket from a hot poured and palletized mold in the second longitudinal path of pallet movement to a cold unpoured and palletized mold in the first longitudinal path of pallet movement. Since the two molds between which the jacket transfer is to be effected are laterally displaced from each other and occupy positions in different laterally spaced apart longitudinal paths of pallet movements, it is necessary for the jacket transfer mechanism to employ a superstructure which bridges or overlies both paths and embodies overhead gripping facilities. Such jacket transfer operations are carried out by first vertically aligning the gripping facilities of the system with the hot jacketed and poured mold in the second path and then lowering such gripping facilities and causing them to engage the jacket on such mold, after which raising of the facilities will cause the gripped jacket to be picked up from the hot mold and raised until the jacket clears the subjacent mold. Thereafter, such gripping facilities with the jacket held thereby are shifted laterally so as to become aligned with the cold unjacketed mold in the first longitudinal path, after which lowering thereof will place the jacket on the cold mold, whereupon release of the gripping facilities will leave the jacket operatively positioned on the cold mold. The, thus, released gripping facilities are again elevated into the confines of the superstructure and indexing of the conveyor system is resumed, thus shifting the hot mold, now relieved of its jacket, longitudinally and rearwardly out of the jacket removal station and shifting the cold mold with the newly applied jacket thereon longitudinally and forwardly out of the jacket-applying station. In known prior art systems, time is lost during performance of the actual jacket transfer operations which includes such steps as opening and closing the jaws of the gripper facilities, as well as shifting such facilities from one path to the other and back again. These problems have been repeatedly addressed in the prior art. Freisen, in U.S. Pat. No. 4,299,269, taught a chain of individually suspended mold-carrying gondolas which is intermittently moved around a closed curvilinear post-suspended track, each gondola being capable of carrying one or more sand molds on pallets, (also known as mold boards). In a preferred form of the invention, each gondola carries two molds, each on a separate pallet positioned end to end across the line of travel of the gondolas, the pallets resting on the gondola floors which are provided with slide members permitting the pallets to be movably positioned as to outer and inner locations.
U.S. Pat. No. 4,422,495, issued to Van Nette, III et al taught a system in which mold carrying cars are moved along a closed loop which projects vertically for minimizing required floor space. The empty cars are vertically raised by a first elevator located at one end of the loop for positioning an empty car adjacent a mold-handling conveyor, whereupon one or more molds are pushed onto the empty car, from which it is transferred into a pre-pour mold storage. From this storage the mold-bearing car is moved forwardly along a guide rail onto a second elevator which lifts the car upwardly adjacent an elevated pouring deck. As the mold is elevated, a jacket and weight are automatically deposited thereon, and the mold is poured while the car rests on the second elevator. The mold-bearing car is then moved forwardly along a guide rail through a jacket-and-weight transfer station. When reaching the end of this station, the jacket and weight are automatically removed and recycled back for positioning on another mold arriving on the second elevator. After the jacket and weight are removed, the mold-bearing car is moved forwardly along the guide rail through a cooling region, which region may be of two levels with the individual cars being positioned on either level by means of elevators. Upon reaching the end of the cooling section, the mold car is transferred onto a third elevator which, when in its raised position, is tiltable so that the mold is dumped from the car, with the car being cleaned by a suitable brush. After dumping, the third elevator is lowered and the mold car transferred onto a lowermost return guide rail which, through a walking beam arrangement, transfers the empty cars back to the first elevator. The return guide rail, together with at least a portion of the rail defining the pre-pour mold storage, extends in parallel relationship beneath the elevated pouring deck so that a maximum number of cars can be recirculated along the path while minimizing the required floor space within the foundry.
U.S. Pat. No. 3,955,613 issued to Lund May 11, 1976 taught using longitudinal and transverse paths which also index alternately, establishes an intersection of a longitudinal and a transverse path such that following a transverse index the intersection will be occupied by a poured mold with jacket and following a longitudinal index the intersection will be occupied by an unpoured mold requiring a jacket.
None of the prior art available for casting in green sand systems solves the problems of speed and flexibility presented above; therefore, a need exists for a novel sand casting system an apparatus for metal jacketed casting.